Re: Mixing OO and DB
Date: Wed, 13 Feb 2008 21:44:38 -0800 (PST)
On Feb 14, 1:54 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "David BL" <davi..._at_iinet.net.au> wrote in message
> > On Feb 13, 9:22 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> >> Perhaps I should clarify: A database is a proposition--a picture of the
> >> universe. There can be many possible pictures of the universe, but only
> >> one
> >> is supposed to be true. A value can appear in many possible pictures, so
> >> it
> >> follows that a value can appear in a possible picture that is supposed to
> >> be
> >> true or in a possible picture that is not supposed to be true, /or both/.
> > Yes, a value can appear in many different contexts. In this
> > discussion I think we need to be very careful with distinguishing
> > between a value, and the appearance (ie encoding) of a value in a
> > particular context.
> >> If a value is a fact, how, then, can it be both true and not true?
> > What does it mean to say a value is a fact?
> I think that's my point.
> >> An
> >> instance of a value, a value in context--the association of a value with
> >> a
> >> picture of the universe--on the other hand, /can/ be a fact because that
> >> association can be with a possible picture that is supposed to be true or
> >> with a possible picture that is not supposed to be true, /but not both/.
> > I think I understand what you are saying, but I would say it slightly
> > differently. Rather than "instance of value" I would say "appearance
> > of value", but only because I'm so used to seeing "instance" used in
> > the context of "instance of a type", but maybe that's my OO background
> > showing through. Instantiation also makes me think of the terminology
> > used for binding variables to values such as when one says a
> > proposition is an instantiation of a predicate.
> I used the term 'instance' to eliminate confusion when there is more than
> one appearance of a particular value in the same picture of the universe.
> For example,
> "Bill Jones married Judy Smith on '1995-06-23' in Cleveland, Ohio."
> "Bill Jones married Sally Martin on '2000-03-15' in Akron, Ohio."
> Here, the value 'Bill Jones' appears multiple times in the same picture of
> the universe, yet due to Leibniz there can still only be one association
> between the value 'Bill Jones' and that particular picture of the universe.
> So there is only one 'instance' even though there can be more than one
> > I also don't see how an appearance of a value itself generally
> > represents a fact (even though it's tied to a context). I can see
> > it's true if you assume the value is a tuple within a relation, but
> > was that your intention?
> The appearance of a value in a proposition that is supposed to be true
> asserts existence. Under an interpretation every constant symbol in a
> proposition is mapped to an individual in the Universe of Discourse. That
> obviously can't happen if any of the individuals do not exist. So it
> follows that every appearance of a value is a mapping from a constant symbol
> to an individual that actually exists.
For a start that assumes domains are strongly typed.
What about an Age domain? Are you suggesting that an Age value maps to an individual in the UoD? I find that extremely counterintuitive.
Often multiple values are required to identify an individual in the UoD.
> >> A value that appears in any possible picture of the universe is a
> >> possible
> >> value. A value that appears in the possible picture of the universe that
> >> is
> >> supposed to be true is an actual value.
> > You've lost me.
> There can be many possible extensions, but only one, the actual extension,
> represents the current state of affairs.
It doesn't seem worth commenting on this given the more fundamental issue that I have above.
> >> Thus a value is just a value without some context. Once a value is given
> >> context, such as being stored in a database, or written down, or
> >> whatever,
> >> then it can be considered information.
> > I think I know what you're saying but I don't like the way you say
> > it. It doesn't make sense to say a value is given a context. A
> > value like the integer 73 doesn't float around and suddenly drop into
> > your database! The value just "is". A database may contain any
> > number of appearances or encodings of the value 73, but the abstract
> > number itself doesn't have a context. It is the appearance of the
> > value that has a context (and can be considered information within
> > that context)
> I think we need to be careful not to mix concepts here. First, it doesn't
> matter whether something is concrete or abstract. "Bill Jones" without a
> context is not data even though "Bill Jones" is concrete.
> Second, can a
> value be a value if the individual it maps to doesn't exist?
A value is a value full stop. It almost sounds like you suggesting the integers spring into existence as they are needed!
> Third, the
> problem is not that the number 73 doesn't have a context--it has many
> contexts, one for each possible picture of the universe in which it appears;
> the problem is that it doesn't have one and only one context.
Ok this is better, because in a previous post I thought you were saying "the context of a value" as if a value only had a single context.
> >> Each atomic value that is in the
> >> database is a datum simply because it is /in/ the database.
> > Agreed. An appearance (ie encoding) of a value has a context and is
> > data.
> Careful. Just because a picture is possible doesn't mean that it is
> supposed to be true, so just because an appearance of a value has context
> doesn't mean that it is data: just because it is possible that I won the
> lotto doesn't mean that I actually did.
Received on Wed Feb 13 2008 - 23:44:38 CST